1. Field of the Invention
The invention relates to digital communication devices, and in particular, to an enhanced error-erasure decoding method applicable to a burst error detection mechanism.
2. Description of the Related Art
In a conventional receiver, various types of noise, distortion, and interference are common factors that deteriorate signal quality to render erroneous outputs. Error-correcting coding (ECC) is a prevalent technique to help a receiver resist the above-mentioned factors, reduce the probability of errors, and enhance the reliability of the outputted data.
Concatenated coding is a kind of error-correcting coding technique that implements multiple levels of coding, such as inner coding and outer coding. For example, convolutional codes or Trellis-Coded-Modulation (TCM) codes could be used as the inner codes, which would help to overcome scattered random errors. Reed-Solomon (RS) codes or BCH codes could be used as the outer codes, which would help to overcome burst errors.
FIG. 1 shows a block diagram of a conventional receiver for decoding concatenated codes. The receiver 100 shown in FIG. 1 comprises a demodulator 110, an inner decoder 120, a deinterleaver 130, and an outer decoder 140. The demodulator 110 receives a radio frequency signal #RF to generate a data stream #S and may comprise components such as synthesizers for frequency down conversion, filters for anti-aliasing, synchronization means for timing or frequency recovery, and an equalizer for compensating for fading or impairment channel effects. After some or all of the above-mentioned operations are performed, the demodulator 110 then generates a data stream #S.
Depending on which kind of inner code is utilized, the inner decoder 120 may be implemented by a convolutional decoder or a TCM decoder, performing inner decoding processes on the data stream #S to generate inner decoded stream #I. Following the inner decoder 120, a deinterleaver 130 deinterleaves the inner decoded stream #I to generate a deinterleaved stream #D. The deinterleaver 130 plays an important role in scattering some kinds of burst noise in order to share the error-correction burden.
The outer decoder 140 performs an outer-decoding process on the deinterleaved stream #D to output receiver output #OUT and could be dependently implemented by an RS decoder or a BCH decoder. For example, when RS codes are utilized as the outer codes, the outer decoder 140 implements an RS error decoder. The outer decoder 140 can correct a maximum of t errors for (n, k, 2t) RS codes. In other words, the outer decoder 140 has an error correction capability of t errors. However, in some communication systems, especially in terrestrial broadcasting systems, complex multi-path channels would induce severe fading or interference so that the equalizer of the demodulator 110 cannot entirely compensate for the fading or interference. In such circumstances, burst noise may cause errors on the inner decoder 120 to propagate to the outer decoder 140, wherein even the deinterleaver 130 cannot scatter them efficiently. Therefore, an erasure marking mechanism is proposed to enhance the capability of error correction.
If the demodulator 110 is able to detect burst noise, and the inner decoder 120 has a mechanism to mark unreliable symbols as erasure indicators, the outer decoder 140 can be upgraded to an RS error-erasure decoder. An RS error-erasure decoder can correct x errors and y erasures for (n, k, 2t) RS codes, only if 2x+y≦2t. In other words, the outer decoder 140 has the opportunity to correct codewords with an actual error number that is larger than t if it is informed with some error locations marked as erasures.
An erasure marking procedure must be performed based on a reliable burst error detection, however, the burst error detection mechanism is currently a preliminary technique. It is therefore desirable to provide an enhanced burst error detector.